1. Field of the Invention
The field of the invention concerns fan motors for use in various types of electronic equipment, more particularly fan motors which may cool heat-radiating electronic parts.
2. Background Information
Conventionally, the overheating of heat-radiating electronic parts has been prevented by installing heat-radiating plates with heat-radiating fins in close contact with said electronic parts. Heat-radiating plates depend on natural heat radiation, however, and therefore have a poor heat radiation efficiency. Furthermore in order to maintain the heat radiation efficiency at a given level, it is necessary to increase the height of the heat-radiating fins, and as a result, such heat-radiating plates are bulky and occupy a large installation space.
Accordingly the present applicant previously proposed a fan motor (Japanese Patent Application No. 6-137701) as a device which is superior to heat-radiating plates in terms of heat radiation efficiency, cost, and size.
Specifically, said fan motor consisted of a rotor which is constructed by installing a plurality of permanent magnets at prescribed relative angles on the circumferential rim portion of a vane wheel, and a stator which is constructed by installing one or more electromagnets and at least one magnetic body on the inside circumferential portion of a casing. A conductive circuit is connected to the field magnetic coils of the electromagnets, and the magnetic body is positioned in a prescribed relatively offset angular position (P) with respect to the electromagnets. Furthermore, a detector which detects when the permanent magnets of the vane wheel are in the vicinity of the relatively offset angular position (P), and which accordingly connects the conductive circuit, is attached to the inside circumferential portion of the casing. When this conductive circuit is in an "off" state, the magnetic force of the permanent magnets of the vane wheel acts respectively on the cores of the electromagnets and the magnetic body so that the vane wheel is offset toward the aforementioned relatively offset angular position (P). When the conductive circuit is in a conductive state, the repulsive force of the electromagnets acts on the permanent magnets so that the vane wheel is caused to rotate.
There may be occasions where the aforementioned fan motor is mounted on electronic parts of audio equipment in which an extremely high sound quality is required. In such cases, even the slight air-cutting noise generated by the fan motor may become an annoyance.
Furthermore, there may be a need to change the blowing direction after the fan motor has been mounted on the electronic parts, which would require either to change the direction of installation of the fan motor, or to alter the wiring of the conductive circuit.
Moreover, the fan motor is constructed so that the proximity of the permanent magnets of the vane wheel to the relatively offset angular position (P) is detected by the detector, and the conductive circuit is switched on only during this period. Accordingly, each time the field magnetic coils are switched off, a surge voltage is generated by the counter electromotive force of said field magnetic coils. There is a danger that this surge voltage might damage electronic equipment.
The present invention has improved upon the aforementioned problems.